The present invention relates to a photometry device applicable to an SLR (Single Lens Reflex) camera, and more particularly to a photometry device with which exposure errors due to a difference of reflectivity of objects having different colors can be compensated.
Recently, reflection type photometry devices have been employed in most of cameras. The reflection type photometry device receives the light, which is reflected by an object and passed through an observing optical system of a camera, using a light receiving element, determines the brightness of the object based on the output of the measured value, and then calculates the exposure value of the camera based on the measured brightness. However, this type of the photometry device cannot detect the color of the object because of its structure. Accordingly, in such a device, the reflectivity of an object is generally assumed to be 18% and the exposure parameter is determined on this assumption. Therefore, regarding a whitish object whose reflectivity is greater than 18%, the determined brightness is greater than the actual brightness. If the camera controls an exposure operation based on the determined exposure value, the object is under exposed. A dark object whose reflectivity is less than 18% is measured to have a lower brightness. Therefore, such an object is over exposed. The difference of the reflectivity of the object may also occur depending on the color of the object. For example, when the color of an object is yellow, the reflectivity may be up to 70%. In such a case, if the standard reflectivity is assumed to be 18%, the exposure value is approximately 2 Ev lower than necessary. If the object color is blue, the reflectivity is approximately 9%. In this case, the object is over exposed by approximately 1 Ev greater than necessary.
Therefore, in the conventional photometry device, the photographer is required to guess the reflectivity of the object. Then, based on the reflectivity determined by the photographer, the exposure is controlled such that, if the object is a whitish or yellowish one having a relatively high reflectivity, it is to be overexposed, and if the object is a blackish or bluish one having a relatively low reflectivity, it is to be underexposed. With this operation, the above-described defects may be solved. However, accurately guessing the reflectivity of the object and controlling the exposure can only be done by experienced and skilled photographers. It is impossible to require all the photographers to do such an operation. Further, it is not preferable that a manual operation of the photographer is required for exposure. Further, if such a manual operation is required, cameras become unsuitable for automatic photographing which is the recent trend.
It may be possible to measure the color of the object, and perform exposure compensation based on the reflectivity corresponding to the measured color. If such a control is performed, an appropriate exposure value seems to be obtained automatically regardless of the color of the object. To perform such operation, a plurality of sensors for colorimetry may be provided inside the camera for selectively measuring different portions of the object. That is, light passed through a photographing lens of the camera is received by the plurality of sensors.
When such a structure is adopted, however, the spectral reflection characteristics of the object and the spectral radiant characteristic of an external light source are overlapped when the colorimetry is performed. Therefore, due to the spectral radiant characteristics of the external light source illuminating the object, it becomes difficult to measure the object color accurately. Then, the compensation amount of the exposure value includes errors, and the appropriate exposure may not be achieved.
It is therefore an object of the invention to provide an improved photometry device with which appropriate exposure values can be obtained regardless of a difference of reflectivity of the objects without being affected by the spectral radiant characteristics of a light source illuminating the object.
For the above object, according to an aspect of the invention, there is provided a photometry device for a camera, which is provided with a normal light sensor that performs a photometry operation with respect to an object, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a plurality of colorimetric sensors having spectral sensitivity characteristics different from each other, the plurality of colorimetric sensors performing a colorimetric operation with respect to an image of the object through a lens of the camera, an external light sensor that measures external light illuminating the object at spectral sensitivity characteristics corresponding to each of the plurality of colorimetric sensors, a light source color compensation amount calculation system that calculates a light source color compensation amount based on light source data, a colorimetric compensation amount calculation system that determines a color of the object based on the metered values output by the colorimetric sensors and compensated using the light source color compensation amount, and that calculates a colorimetric compensation amount based on the judged color, and a colorimetric compensation system that compensates for the exposure amount based on the colorimetric compensation amount. In such a photometry device, a predetermined fixed value is used as the light source data, and, if a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor is greater than a predetermined reference value, the colorimetric compensation amount is forcibly set to zero.
Alternatively, if a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor is greater than the predetermined reference value, operations of the colorimetric compensation amount calculation system and the colorimetric compensation system are not performed.
Further alternatively, the colorimetric compensation amount is compensated based on a coefficient obtained from a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor.
In each case, the photometry device may further be provided with a storage device, and light source data corresponding to an output of the external light sensor may be stored in the storage device. In this case, the fixed value can be calculated from the light source data stored in the storage device.
According to another aspect of the invention, there is provided a photometry device for a camera, which is provided with a normal light sensor that performs a photometry operation with respect to an object, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a plurality of colorimetric sensors having spectral sensitivity characteristics different from each other, the plurality of colorimetric sensors performing a colorimetric operation with respect to an image of the object through a lens of the camera, an external light sensor that measures external light illuminating the object at spectral sensitivity characteristics corresponding to each of the plurality of colorimetric sensors, a light source color compensation amount calculation system that calculates a light source color compensation amount based on light source data;
a colorimetric compensation amount calculation system that determines a color of the object based on the metered values output by the colorimetric sensors and compensated using the light source color compensation amount, and calculates a colorimetric compensation amount based on the judged color, and a colorimetric compensation system that compensates for the exposure amount based on the colorimetric compensation amount. In such a device, a metered value of the external light sensor is used as the light source data, and if a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor is greater than a predetermined reference value, the colorimetric compensation amount is forcibly set to zero.
Alternatively, a metered value of the external light sensor is used as the light source data, and if a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor is greater than a predetermined reference value, operations of the colorimetric compensation amount calculation system and the colorimetric compensation system are not performed.
Further alternatively, a metered value of the external light sensor may be used as the light source data, and the colorimetric compensation amount is compensated based on a coefficient obtained from a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor.
According to a further aspect of the invention, there is provided a photometry device for a camera, which is provided with a normal light sensor that performs a photometry operation with respect to an object, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a plurality of colorimetric sensors having spectral sensitivity characteristics different from each other, the plurality of colorimetric sensors performing a colorimetric operation with respect to an image of the object through a lens of the camera, an external light sensor that measures external light illuminating the object at spectral sensitivity characteristics corresponding to each of the plurality of colorimetric sensors, a light source color compensation amount calculation system that calculates a light source color compensation amount based on light source data, a colorimetric compensation amount calculation system that determines a color of the object based on the metered values output by the colorimetric sensors and compensated using the light source color compensation amount, and calculates a colorimetric compensation amount based on the judged color, and a colorimetric compensation system that compensates for the exposure amount based on the colorimetric compensation amount.
In such a device, one of the metered value of the external light sensor and a predetermined fixed value is selected as the light source data in accordance with a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor.
Alternatively, a value within a range between the metered value of the external light sensor and a predetermined fixed value is determined as the light source data in accordance with a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor.
Optionally, the photometry device may be provided with a storage device, in which light source data corresponding to an output of the external light sensor is stored, and the fixed value is calculated from the light source data stored in the storage device.
In the above described photometry devices, each of the normal light photometry sensor and the plurality of colorimetric sensors may have a plurality of photometry areas. In such a case, the colorimetric compensation amount calculating system determines a color for each of the plurality of photometry areas and further determines a colorimetric compensation amount for each of the plurality of photometry areas based on the determined color. Further, the colorimetric compensation amount calculating system may determine a colorimetric compensation amount for the entire object based on the colorimetric compensation amounts for the plurality of photometry areas.
Still optionally, in the above described photometry devices, each of the normal light photometry sensor and the plurality of colorimetric sensors may include a plurality of photometry areas. In this case, the colorimetric compensation amount calculating system may determine a color for each of the plurality of photometry areas and further determine a colorimetric compensation amount for each of the plurality of photometry areas based on the determined color. Further, the colorimetric compensation amount calculating system may compensate for the photometry value for each of the plurality of photometry areas based on the colorimetric compensation amount, and determine an exposure amount for the entire object based on the colorimetric compensation amounts for the plurality of photometry areas.
Further optionally, in the photometry devices described above, the normal light photometry device and the plurality of colorimetric sensors meter light reflected by the object and passed through the photographing optical system of the camera, and the external light sensor meters light reflected by the object but not passed through the photographing optical system of the camera.
In this case, the normal light sensor may include a normal light photometry sensor, the spectral sensitivity characteristic of which has a peak sensitivity at a wavelength within a range from 500 nm through 600 nm, and the plurality of colorimetric sensors may include a blue light photometry sensor for metering blue light component, a green light photometry sensor for metering green light component, and a red light photometry sensor for metering red light component. Further, the external light sensor includes a photometry sensor having photometry areas for metering blue, green and red light components, respectively.
The plurality of colorimetric sensors and the normal light sensors may optionally include photometric elements having the same photometric characteristics.
Further, the normal light photometry sensor may function as the green light sensor, and wherein output of the green light sensor is used as the output of the normal light photometry sensor.
According to a further aspect of the invention, there is provided a photometry device, which includes a normal light sensor that performs a photometry operation with respect to an object, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a plurality of colorimetric sensors having spectral sensitivity characteristics different from each other, the plurality of colorimetric sensors performing a colorimetric operation with respect to an image of the object through a lens of the camera, an external light sensor that measures external light illuminating the object at spectral sensitivity characteristics corresponding to each of the plurality of colorimetric sensors, a light source color compensation amount calculation system that calculates a light source color compensation amount based on light source data; and a colorimetric compensation system that compensates for the exposure amount, procedures for compensating for the exposure amount being varied depending on a difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor.
Optionally, the colorimetric compensation system does not substantially compensate for the exposure value if the difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor is greater than a predetermined threshold value.
Still optionally, the colorimetric compensation system may determine a coefficient used for calculation of colorimetric compensation amount in accordance with the difference between the exposure value obtained from the output of the external light sensor and the exposure value obtained based on the output of the normal light photometry sensor is greater than a predetermined threshold value.
Further optionally, each of the normal light photometry sensor and the plurality of colorimetric sensors has a plurality of photometry areas, the colorimetric compensation amount calculating system determining a color for each of the plurality of photometry areas and further determining a colorimetric compensation amount for each of the plurality of photometry areas based on the determined color, the colorimetric compensation amount calculating system further compensating for the photometry value for each of the plurality of photometry areas based on the colorimetric compensation amount, and determining an exposure amount for the entire object based on the colorimetric compensation amounts for the plurality of photometry areas.
Still optionally, the photometry device may further include a light source color compensation amount calculation system that calculates a light source color compensation amount based on light source data, and a colorimetric compensation amount calculation system that determines a color of the object based on the metered values output by the colorimetric sensors and compensated using the light source color compensation amount, and calculates a colorimetric compensation amount based on the judged color.